Thanks for all the advice,changed the 3 port valve as it looked as if it had been played with. Found the problem was a faulty terminal box. Now works perfectly.
When I turn the power on the pump starts to run straight away. When I press the heating button on the horsttmann c27 controller both heating and water lights come on and have no control via room or cylinder stats so boiler and pump just keep running with no control. checked a y plan wiring...
